MHC class I tetramers have been used extensively to directly identify and characterize antigen specific CD8 T-cells in the setting of infection, malignancy and graft versus host disease. Producing MHC class I tetramers requires the purification of recombinantly expressed class I heavy chain and beta-2-microglobulin, in vitro folding of these proteins with antigenic peptides, enzymatic biotinylation and complex formation with fluorescently labeled streptavidin. We have established a protocol for the reproducible and reliable production of high quality tetramers using the following MHC class I proteins: HLA A1, A2, A3, A11, B7, B8, B27, B35 and H2-Kd, Kb, Db and Ld. The HLA-tetramer core will generate MHC class I tetramers for projects described in this program. The core will incorporate quality control assays at all major steps during tetramer production and will test the specificity and sensitivity of tetramers when CD8 T-cell lines are available. MHC class I tetramer production is time consuming and requires significant technical training and expertise. The HLA-tetramer core will greatly facility the production of tetramers for the projects of this program.